All About Insulin [What It Is, How It Works, And More]


Insulin is so hot right now.

More than 1 in 3 Americans are prediabetic, with most not even aware of the problem.  

In the fitness industry, you’ll mostly hear talk about insulin in the low-carb/keto/carnivore communities.  They will claim insulin is the root of all evil and you should avoid elevating it at all costs. 

However, if you want to build muscle, it’s necessary, and if you want to eat a well-rounded diet you need to have good insulin sensitivity.   

Cutting out all carbs is just a poor band-aid and doesn’t get to the root of the issue if you have poor insulin sensitivity. 

Backing up a bit, let’s explain what insulin is, and why we need it.

When you eat carbohydrates, those carbs are converted to glucose and you get a rise in blood glucose (meaning sugar in your blood).  Your body doesn’t like having that sugar level too high, so your pancreas secretes insulin. 

Insulin is a hormone that takes the glucose in your blood to the cells of the muscle, fat, and liver to be stored or used for energy.  

→ Good insulin sensitivity: Your blood glucose gets cleared quickly and taken where it needs to go.  

→ Poor insulin sensitivity: Your pancreas has to pump out more and more insulin to get the job done. Eventually, it stops secreting enough, and that’s when you have type 2 diabetes. 

You can think of insulin as a city bus.  

Glucose gets on, and insulin shuttles it to its stop in the appropriate cell.  

Having good insulin sensitivity means the bus is on time and able to accommodate all its glucose passengers.  

Poor insulin sensitivity means the pancreas has to send out more busses to get the glucose passengers to their destinations. 

Insulin resistance has several health consequences. Poor insulin sensitivity is associated with...

- High HDL 

- High blood pressure 

- Damaged blood cells 

- Cataracts and glaucoma 

- Risk of infection 

- Nerve damage

Improving insulin sensitivity is not only important for health and avoiding diabetes, it’s necessary for building muscle and losing fat too. 

Insulin’s Role In Muscle-Building

When you eat carbs or protein, your pancreas releases insulin, which goes to the muscle cell, knocks on the door, and the cell opens up for carbs, protein, and creatine to enter.  

This process also increases muscle protein synthesis and decreases muscle protein breakdown*, and increases blood flow to the muscles. 

[*Muscle protein synthesis is a process in which protein is produced to repair muscle damage caused by intense exercise. It is an opposing force to muscle protein breakdown in which protein is lost as a result of exercise.]

This is why professional bodybuilders inject exogenous insulin, however, this is at very high doses and is NOT recommended as it can be fatal. 

Multiple studies (HERE, HERE, and HERE) have shown that having a high carb diet is superior to low-carb diets for building and maintaining muscle. This makes sense for a few reasons:

→ FIRST: Having carbs means you’ll have more energy in workouts, and more likely complete more reps, accruing more volume in your training 

→ SECOND: Having carbs means you’ll be getting an insulin response, which we’ve just discussed helps build and maintain muscle 

→ THIRD: Having carbs will blunt cortisol, a catabolic stress hormone, and increases testosterone, both of which will help build and maintain muscle

For these reasons, we recommend setting your protein at about a gram per pound, setting your fats close to the minimum of 0.3-0.4 grams per pound, and getting the rest of your calories from carbohydrates. 

Immediately pre-and post-exercise are the best times to include high carb meals because insulin sensitivity is improved after a workout that depletes the glycogen stores in the muscle.  

In fact, a glycogen depleting workout can improve insulin sensitivity for the next several hours.

Does Insulin Prevent Fat Loss?

While insulin is elevated it inhibits lipolysis (fat-burning), and also has the job of taking excess glucose to the fat cells for storage.  This is why insulin gets a bad reputation.  

But it’s very important to know that if you’re not in a calorie surplus, you won’t be storing fat because you won’t have a surplus of energy that needs to be stored.  

As mentioned above, pro bodybuilders take extreme doses of insulin, and they’re the leanest athletes in the world, so if it was the road leading straight to body fat they wouldn’t be taking it.

This graph from shows how insulin rises and falls and when fat burning is blunted:

During and after a meal (green) you have elevated insulin, and may not be burning fat at that moment, but meals are followed by times where you dip back into fat burning before eating again, and then have a longer period of time overnight where you are burning fat while you sleep.  

When you are in a calorie deficit, the blue fat-burning time periods will be larger than the green, fat-storing time period and you will have a net fat-loss for the day.  

On days you’re in a calorie surplus, the green fat-storage time periods are longer and will net more than the blue fat-burning time periods.  This is true whether you are eating a high carb, low-fat diet, OR a low carb, high-fat diet.

In fact, insulin is not only NOT the villain it is believed to be for fat-loss, it can actually suppress appetite.  

When you get a rise in insulin (if you aren’t type-1 diabetic) you’ll also get a rise in a hormone called amylin which decreases appetite and stimulates lipolysis, the breakdown of fats into fatty acids.

Controlling and Improving Insulin Response

Having a healthy insulin response, as discussed above, is a natural occurrence in a healthy, functioning body.  

Having spikes in insulin isn’t a negative thing in regards to your health and it can improve satiety and help build muscle mass, which in turn helps improve all kinds of health markers. 

That said, we want to maintain good insulin sensitivity to avoid negative health outcomes.  

Poor insulin sensitivity tends to come along with other metabolic diseases in a group.  These can include...

- Obesity 

- High blood pressure 

- High cholesterol 

- Type 2 diabetes

When several of these are present it is often referred to as metabolic syndrome. Symptoms of insulin resistance are... 

- Waistline over 40 inches in men and 35 inches in women 

- High blood pressure (over 130/80) 

- High fasted glucose (over 100mg/dL) 

- High triglycerides (over 150 mg/dL)

- Low HDL cholesterol (under 40 mg/dL men, and under 50 mg/dL women) 

- Skin tags 

Risk factors of having poor insulin sensitivity are...

- Obesity 

- Inactive lifestyle 

- Chronic high carb diet without glycogen depleting exercise 

- Smoking 

- Family history 

- Poor sleep 

- Age 45+

Improving Insulin Sensitivity

Improving insulin sensitivity may not be easy, but it IS simple.  Doing the same things that promote “general health” will also improve insulin sensitivity.


Keeping body fat under control is a major factor in improving insulin sensitivity.  

A leaner person is usually a more insulin sensitive person.  If you are currently overweight or obese, your first step is to create a calorie deficit (burn more calories than you eat) and to start an exercise regimen.  

To have accountability and a personalized plan to help you do this, you can apply for coaching to have our coaching team guide you. 


The amount of muscle mass a person has is inversely related to insulin sensitivity and prediabetes.  An article called “Muscle Mass Knocks Out Insulin Resistance” cites a study from 2011 saying “For every 10% increase in muscle mass ratio, there was a 14% reduction in HOMA-IR and a 23% reduction in combined diabetes prevalence.” 

You can think of muscles as big storage bins for glycogen.  The bigger your muscles, the larger your storage capacity. When you eat carbs, they’re converted to glycogen and either taken to the muscle or the fat cell.  

The bigger the muscle, the more carbs can be stored within the muscle before needing to resort to the fat cells.  

Let’s say for example we have two athletes.  One has a lot of muscle mass and one doesn’t.  The athlete with a lot of muscle mass may be able to eat 350-400g of carbs per day, whereas the smaller athlete may only have the capacity for 250g of carbs per day.


This one may seem obvious, or a repeat of the first two points but it deserves it’s own spot.  

You can build muscle mass and even lose weight without being active enough throughout the day.  It’s not enough to get your workout done and then sit at your desk the rest of the day.  Getting more active includes the other time outside of your training session.   

This doesn’t mean you need to be working out all day.  

A study from 2016 called “Breaking sitting with light activity vs structured exercise: a randomized crossover study demonstrating benefits for glycaemic control and insulin sensitivity in type 2 diabetes” showed that breaking up your day of sitting with standing and light-intensity walking significantly improved 24-hour glucose. 

Another study from the American Diabetes Association found that three 15 minute walks after meals was an effective treatment for diabetics.


Getting just 5 hours per night of sleep for a week significantly reduced insulin sensitivity in a study by the American Diabetes Association, and people with sleep disorders are twice as likely to develop type 2 diabetes. 

Ideally, you should sleep between 7-9 hours per night. 

The most helpful thing for our clients has been establishing a good nighttime routine. 

Here’s what we suggest: 

Consider the last hour before bed your "wind down time" 

→ No TV, stay off your phone for AT LEAST the last 30-minutes before bed 

→ Don't touch your bed except to sleep in it 

→ Try to avoid as many artificial lights as possible. Doing things by candlelight helps your Circadian Rhythm, but is usually a bit unrealistic. Try just using a lamp light instead of a fully lit room.

In the last 30 minutes before you go to bed: 

 1. Journal - do a “brain dump” for anywhere from 5-20 minutes. Writing out all your thoughts prevents a racing mind when trying to fall asleep. 

2. Meditate  Apps can be helpful if you’re new to meditation.  App suggestions: 

- Calm 

- Headspace 

- Brain. FM 

3. When you get in bed stay off your phone, and just focus on belly breathing.  

How to do belly breathing: 

Put a hand on your belly. Inhale through your nose for a 5 count - focus on feeling your belly fill with air. Hold briefly. Exhale through your mouth for a 5 count. Focus on completely emptying your belly. Repeat x10.


Stress reduces your body’s ability to regulate glucose.   

When you are stressed you release stress hormones called cortisol and glucagon.  

This state is called sympathetic, or “fight-or-flight”.  The stress hormones break down glycogen (stored sugar) into glucose (blood sugar) so it has the energy for “fight-or-flight”.  This is great if the stress you’re encountering is a bear...  but less ideal if the stress you encounter is an email from your boss while you’re parked in your work chair. 

Luckily a lot of the same activities that we’ve already discussed can also help address high stress: 

- Meditation 

- Walking 

- Belly breathing 

- Journaling 

You can also add on any of your favorite self-care strategies that relieve stress for you, and remove any sources of stress that are under your control.


Whole foods (meaning foods that at one time grew from the earth or had a face) are usually not fast-digesting carbs. Eating meals that include protein, fat, and fiber will slow down digestion, which in turn slows the release of insulin. 

Another bonus of cooking meals at home comprised of whole foods is the spices and herbs that you probably use to flavor meals. 

Many different herbs and spices have been found beneficial to blood sugar control and insulin sensitivity. 

If you are prediabetic and concerned about your insulin sensitivity, give these strategies a shot and see the difference it makes in your glucose numbers. 

If this is something you are interested in learning more about, or want a coach to guide you through your fitness journey to improve your insulin sensitivity and health, apply for coaching with our team.  

While poor metabolic health and insulin resistance is something that absolutely is common, it is under your control and we can help you do something about it.

about the Author

Andrea Rogers is a certified nutrition coach, personal trainer, and coach for BairFit. Follow her on Instagram for more helpful training & nutrition content.

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